I. Field of the Invention
This invention relates generally to electrosurgical apparatus, and more particularly to a blade adapted to be used as an electrosurgical scalpel for parting tissue using radio-frequency energy.
II. Discussion of the Prior Art
In a co-pending application Ser. No. 56,434, filed June 1, 1987 now U.S. Pat. No. 4,802,476 issued May 7, 1989, entitled "ELECTROSURGICAL INSTRUMENT" and which is assigned to the assignee of the present invention, there is described an electrosurgical instrument comprising a blade and a blade handle in which the blade is adapted to snap into the handle, and when so positioned, establishes an electrical connection between an RF power source and metallized electrode surfaces formed on the blade. In that application, the blade is fabricated from a metal blank, the metal being overlaid on each side with a suitable insulation, and deposited atop the insulation layers are printed conductors. When the blade is appropriately energized, an RF field is established between the printed conductors and the metal blank. This style of blade is not altogether satisfactory, due primarily to blade erosion. The radio-frequency arc discharge between the printed conductors on the blade and the blade blank itself causes pitting, leading to a relatively short blade life.
In accordance with the present invention, the blade blank is a thin ceramic substrate having a proximal handle receiving segment and an integrally formed distal segment, which is preferably somewhat triangular in shape, but with a rounded apex at its distal end. A portion of the blank, including the adjacent sides and the rounded tip, are beveled at a predetermined angle to the plane of the blank and, during manufacture, a metallization pattern is vacuum-deposited or otherwise formed onto the major surfaces of the blank so as to extend over the beveled surfaces The blank with the metallization on it is then subjected to a backgrinding operation to form a blunt working edge which is free of metallization and which maintains a predetermined spacing between the conductive patterns on the opposed side surfaces of the blank.
The ceramic substrate permits higher temperatures to be used without destruction of the blade surface, thus leading to a longer blade life as compared to those having a metal blank. The ceramic substrate also lends itself to metal deposition processes now commonly available and widely used in the fabrication of integrated hybrid circuits.
In accordance with one embodiment of the invention, the pattern of metallization on the ceramic blank creates an open loop overlaying the beveled edges of the blank. This open loop is then connected by an integrally formed trace extending to the proximal end portion of the blade where it mates with the electrical connector in the blade handle. By providing an open loop tip, the overall capacitance of the blade is reduced, thus reducing the amount of energy wasted in the delivery of power to the load.
In accordance with another aspect of the invention, rather than providing a metallization pattern including a loop conductor, the beveled surfaces of the blank are, instead, entirely covered with metallization. This has the advantage of providing improved heat conductivity away from the blade edge and through the metal trace to a suitable heat sync. As such, the metallization does not become overheated which could result in unwanted melting of the metallization pattern or the oxidation thereof.
Irrespective of the metallization pattern employed, the blade of the present invention may be subjected to a further processing operation prior to the backgrinding of the edges in which a glass-like layer of insulation is provided as an overcoat to the blade blank and the previously applied metallization pattern. By proper choice of the overcoat material, it is possible to minimize adhesion of the blade to tissue during its use. An overcoat possessing good thermal insulation and high impedance characteristics results in much improved performance of the blade in its electrosurgical use.